1. Field of the Invention
The present invention relates to a method for manufacturing a printed circuit board to become a material of an electronic component such as a TAB tape, COF tape and the like, and relates to a printed circuit board obtained by the manufacturing method. More particularly, it relates to a manufacturing method of a printed circuit board in which metal residue between wirings can be removed without side etching of a copper layer in an inexpensive and simple process by applying predetermined etching to adhesiveless copper clad laminates, and a pattern having sufficient insulation reliability can be formed in a micro wiring working, and relates to a printed circuit board obtained by the manufacturing method.
2. Description of the Related Art
In general, circuit boards used for manufacturing a flexible circuit board are roughly classified into adhesive copper clad laminates in which a copper foil to become a conductor layer is bonded onto an insulator film using an adhesive (See Japanese Patent Laid-Open No. H6-132628, for example) and adhesiveless copper clad laminates in which a copper coat layer to become a conductor layer is directly formed on the insulator film by a dry plating method or a wet plating method without using an adhesive.
With the recent trend of high-density electronic equipment, a circuit board having a wiring width set with a narrow pitch has been in demand, and in this case, in manufacturing the adhesive copper clad laminates, when a circuit board is to be manufactured by forming a wiring portion through etching according to a desired wiring pattern on a copper coat layer formed on an insulator film as a board, there is a problem that since etching on a side face of the wiring portion, which is so-called side-etching, is caused, a sectional shape of the wiring portion can be a splay-out trapezoid easily.
Therefore, in order to satisfy such a demand, the adhesiveless copper clad laminates has become a main stream at present instead of the prior-art bonded copper foil (adhesive copper clad laminates).
In order to manufacture the adhesiveless copper clad laminates, an electric copper-plating method is employed as means for forming a copper coat layer with a uniform thickness on an insulator film. In order to carry out the electric copper plating, conductivity is given to the whole surface by forming a metal layer of a thin film on the insulator film on which the electric copper plating coat is to be applied and the electric copper plating processing is applied thereon in general (See Japanese Patent Laid-Open No. H8-139448, for example). Also, in order to obtain the thin-film metal layer on the insulator film, dry plating methods including vacuum deposition, ion plating and the like are used in general.
In the above, adhesion between the insulator film and the copper coat layer is extremely weak since a fragile layer such as CuO, Cu2O and the like is formed on their interface, and in order to maintain adhesion strength with the copper layer required for the printed circuit board, a Ni—Cr alloy layer is provided as a base metal layer between the insulator film and the copper coat layer (See Japanese Patent Laid-Open No. H6-120630).
Here, in order to form a wiring pattern on a two-layer plated circuit board with a subtractive method, an iron (III) chloride solution in which iron (III) chloride (FeCl3) is dissolved in water or copper (II) chloride solution in which copper (II) chloride (CuCl2 2H2O) is dissolved in water and an appropriate amount of hydrochloric acid is added is used as an etching liquid for conducting etching, for example. In the etching method using these etching liquids, sufficient etching effects can not be obtained in some cases since etching of the base metal layer such as Ni—Cr alloy and the like remains between wirings.
Moreover, in the recent flexible circuit boards, a pitch of the wirings becomes narrower with the trend of higher-density of the wiring pattern, and use under a high voltage has been required with higher functionalities. As a result, the insulation reliability has become more important in the printed circuit board in use, and as an index of this characteristic, a high-temperature high-humidity bias test (HHBT) and the like are conducted.
However, if the etching residue of the base metal layer such as Ni—Cr alloy and the like has been caused when etching of the two-layer plated circuit board is carried out using the above etching liquid, the high-temperature high-humidity bias test (HHBT) might shorten the adjacent copper wirings due to the etching residue of the Ni—Cr alloy layer, which prevents realization of a high insulation resistance and causes defective, which is a problem.
Thus, as one of means for realizing the insulation reliability, the above-mentioned remaining base metal component between wirings needs to be removed.
In order to correct such a trouble, in Japanese Patent Laid-Open No. 2005-23340, for example, dissolution of the etching residue of the Ni—Cr alloy by treatment using one or two types or more of acid etching liquid containing hydrochloric acid and alkali etching liquids such as potassium permanganate solution and the like after treatment with the iron (III) chloride solution or copper (II) chloride solution containing hydrochloric acid. In this case, the etching residue of Ni—Cr alloy can be removed by a method with less side-etching of the copper wiring.